A functional module is a collection of molecules that interact with each other to accomplish a biological function. This group will study the structure, function, and evolution of the mating module from budding yeast, combining experiment and theory to reap the full benefit of these complementary approaches. The proposed work has four aims: 1) To use systematic genetic approaches to identify, characterize, and analyze new genes involved in mating. 2) To monitor and dissect the function and mechanism of the mating module. Theoretical analysis suggested and experiment has confirmed that individual yeast cells shows a switch-like response to pheromone treatment. The group will investigate this response and use a variety of techniques to figure out how cells detect very shallow concentration gradients over a wide range of pheromone concentrations. 3) To investigate the robustness of mating. The group will ask how quantitative variation in one or more parameters of the mating module affect its performance, by controlled perturbation of the four protein kinases in the module. They will monitor multiple aspects of mating, including mating efficiency, mating discrimination, chemotropism, cell cycle arrest and, gene induction to ask if mating is more robust to perturbation than the various processes (arrest, gene expression, chemotropism) that induce it. 4)To evolve the mating module in three directions: a) Speciation (altered specificity) to create novel budding yeast populations that mate within themselves but not to the lab strains they were derived from. b) Altered function (altered logic). At present, pheromone signaling is rapidly reversible, but it will be evolved so that transient exposure to pheromone leads to prolonged activation of the pathway. c) Cross-communication (altered inter module connectivity). Cells will be evolved so that the input of one pathway becomes connected to the output of another.